June/July timeframe is generally when the candidate portal gets updated for the actual application after you have finished the pre-candidate questionaire or applied to SLS
I'm not positive but I'm pretty sure I had my application for the class of 2015 done by July 1st, so it probably opened about a week earlier. I remember checking my portal a few days after I got back from SLS and being surprised that it was up.
USMA accepts with a rolling admissions board, unlike most colleges (or at least the other's I applied to) so basically, as long as your app is done and you have a nomination you are admissible that day.
The earlier the better because you will be competing with a smaller pool of applicants. 1/10 odds are better than 1/10k.
I feel like USMA (and all the service academies) should mandate congressional offices to have all of their nominations turned in on the same day so candidates aren't held back by that.